fix ParsedRequirement object has no attribute 'req'

[tombradford]

fallback to use ParsedRequirement.requirement if the setup.py fails with an attribute error.

tested with:

• python 2.7.15
• python 3.6.3
• python 3.8.5

how to replicate:

git clone https://github.com/DRL/blobtools
cd blobtools
python setup.py install --user

error:

Traceback (most recent call last):
  File "setup.py", line 18, in <module>
    reqs = [str(ir.req) for ir in install_reqs]
  File "setup.py", line 18, in <listcomp>
    reqs = [str(ir.req) for ir in install_reqs]
AttributeError: 'ParsedRequirement' object has no attribute 'req'

supporting docs: https://stackoverflow.com/questions/62114945/attributeerror-parsedrequirement-object-has-no-attribute-req

[BioLaoXu]

Downgrading pip to 20.0.2 worked